Tor is an anonomizing proxy, see their list of usage
scenarios if you want more details. A basic Tor client is
extremely easy to set up on Gentoo, just emerge net-misc/tor,
possibly tweak the stock /etc/tor/torrc, and fire up the connection
with

To use your new Tor "proxy" with Firefox, go to
Edit->Preferences->Advanced->Network->Connection->Settings->Manual
proxy configuration and set

SOCKS host: localhost
Port: 9050
Version: SOCKSv5

To use remote DNS, enter about:config in the address bar, set the
filter to dns, and set network.proxy.socks_remote_dns to true by
double clicking.

To disable cookies, which would allow the sites you're connecting to
to track you as your exit IP changes, go to
Edit->Preferences->Privacy, select Firefox will: Use custom
settings for history, and make sure Accept cookies from sites is
unchecked.